Telephone system



May 6, 1930. v. s. T'HAR'P 1,757,101

v. TELEPHONE SYSTEM Filed April 6, 1929 2 sheets-sheet 1 F IG l OEIGINATING EXCHANGE 1h- -v-uo--H Kl) May 6, 1 930.

FIG. a

TANDEM v EXCHANGE V. s. THARP TELEPHONE'SYSTEM Filed April 6, 1929 2 sneek-sheet 2 I l 4| Imran E111- Patented May 6,1930

, vfulsu'ran s'rgrus` .PfArEpN-rOFFICE' L "VICTOR s. THARP, or ELMHURST, ILLINOIS, Assienon To RESERVE HOLDING coM- I PANY; or CHICAGO, rumors, A conrone'rronor nnLAWAnE' TELEPHONE SYSTEM Application' fue@ April 6,'

Y The present invention relates to telephone p systems 1n general, but `1s concerned morel particularly with multi-office automatic telephone systems; and thelbroad general object k5 isthe` productionk of new-and improved trunk circuits for use 1n connectionivwith the-' 1nter.`

office Vtrunk lines wherebya connection set up trom an originating automatic exchange througha tandem; automatic exchange to a. toll board ismalntained` intactas longas the ,Y connection is maintained in van'answered state by the operator at the-tolliboard, eventhough` the receiver is replaced at the calling sub-A station.

'A feature of the present invention is `that the holding operation is-carried out over `a twosconductor'trunkV line without resorting b to special ground connections or Vspecial bat-v tery connections-at either end of the 'trunk `saline. g Other objects and features, which are more or less incidental to the foregoingwill' becomeapparentupona further perusalofthe f specification'.

Referringv now to the drawings lcomprising Figs. 1.; 2, and 3, Figs. 1 and 2. show bymeans o'f theusual circuit diagrams` certain ap-L paratus of a telephone system embodying'the features of the inventionyand Fig. .3 shows a desirable modification ofthe apparatus;

shown inFigl 2. The invention having of the apparatus shownwill now -be given. `l For the above purpose it will be assumed Athatthe subscriber at theV substation shown in the upper left handcorner of 1 desires Vto extend a connection which must be completed through the l' toll recording` board- 40 shown in-Fig. 2.`

Setting operation Y lllhcn' the receiver isremoved at the calling Y signedto the toll recording board isldialled,

the selector S1` responds in the usual manner :fp

wr and extends theconnection to an trunk been described.genf 4erally a detailed descriptionfof the operation;

A1929;zserialfNoQstaunt-f4 l lineein the'required group, such as ,they trunk line TL1,by wayof a repeater, Vsuch as 'therepeateriR.: `It will be assumed that' the v trunk line TL1 is the virstfone found to beidle,

and that it Vis consequently seized. by way of conductors101,102,.and'103. Y

line'relaylOL'of the VrepeaterR operateslov'er line and closesa circuit'at its lower armature V- for relay 111 by wayiof armature113,normal.'4

Relay .111 operatesand at its'upperarmature" `Vplaces aground vpotential on 'release'trunk conductor 102 so as tofform a holding 'circuit for the selector S1 and for the line switch LS.

conductors 101 and 103 `andover the'v callingy "A ;6O

-At its Vupper armature, relay 104.- closes a ridge acrossl the conductors of the trunk line TL?, whichbridge includes the upperl and 'lower' right-handrepeating-coil windings andthe upperwindingof relay 107,.which is shunted. around the lcondenser 115 by way of the 'inner upper armature, normal, orelay 310,6;5Rel'ay -107 energizes in this'bridge in c series with the line relay (not'shown) ofthe selectorS2-Fig. 2 and opens a point in the 'circuit ofrelay 108, which wouldotherwise-be closed at the .inner'lower armature of rela) l 1072through contactscof relays 111 and 106. It will be notedfthatthe circuit for relay 111 is closedV at the lower armature fof relay 104V atfthe same time that the circuit for relay 107 lis closed'at thejupperarmature ofrelay 104.

Consequently,relays 111 and 107fop`erate'at about the same time.` Inl case relay T107 'op- --eratesslightly .afterfrelay 1,11 has operated, Arelay r108 `.doesnot respond at this time owing, Sto the factthat itisstiiiiyadjusted, which ca-uses thejactual operation l'ofthe V'relay to kbe'delayed until the currenthas risen to almost-fitsfull Value,`.which requires quitera l substantial fractionofga second.`

. Thedistant srelectorvS2 is prepared for opera-tion in the usualmanner responsive to the .currentow over the .trunk lineTL inseries withtheline relay.y .y y y Y E When lthe calling subscriber dials the second andflast digit in thenumber assigned to thev 'toll vrecording operator,` the circuit of Y relay 20,4 `.isinterrupted.'by,the callingdevice Y Cl)` a number vofftirnes corresponding to thedigit dialled; Each time itsciicuitis inter- 1 rupted, relay 104 falls back and Opens at its upper armature the bridge across the conduc f tors oic the trunk liiieV TL with the result that the distant selector S2 isoperatedin the usual manner. At its lower armature, Yrelay 104 opens the circuit of tlies'low acting release lay 105 responds at the beginning ottheseries maintain the 'relay operated While its circuit 20 its-cerdas indicated;V 1 This renders'the relay relay11 eachY time it falls back, and itcompletes a circuit Vthrough the lower armature v`of relay 1111aiid the lower armature ofjrelay 106 forthe seriesfresp'on'ding relay 105. Re-

'of impulses, an'd,'being slow-acting, remains "operated throughout the series. Y, Uponl oper-f 'atiiig,ielay 105 shunts the right-hand repeating-coil'vvindiiigs atitsupper and lower arinatures, and at itsv inner lower a'ririaturer it closes'a-holding circuit forrelay 10'( so Vas to is being interrupted at' the upperi armature of relay 104. lt-'Awill benotedftliat relay107 is provided with la-'copper sleeve surrounding slow in releasinv so that it does'not fall back D n a u u responsive to the openingof its 'circuitat the upper contacts relay'vlOl vbefore relay A105'- responds to the closure icifit's circuit'at the lower armature of relay104 and closes the i aboif'einentionedvholdingcircuit forv relay l viv"` "7. v Y

10'?.V i w.- f

t `the end of the digiti, relaylOLl cornes to rest in an energized condition and relay 105 falls'bacli Relay-107 is `held'up through its upper Winding.v y l p f In the tandem exchange, the selector S2 responds to the second and last digitfin the num`` ber by raising its Wipers opposite the" desired 1 level or" bank contacts and in searching for 'an idle trunk in the'usual manner.V It Will'be assumed that the trunklinefllli, ,reached by Way of the trunlrcircuit TG1, is the first onel found to be idle. In this case thistrunl. lineis seized by the selector S2 by Way of conductors 201, 202, and 203.3 When this seizure takes place, the circuit of relay ,10'Z'jiii'tlhe re-V peaterrR Vis transfer-red tromA the line lrelay Y (not shown) of the selector `'Si kto linerelay relay V204-, andrelay 204operatesj and closes.V

204- oflthetrunlr circuit TG1 ybyiiva-y' of con'- ductors 201 and 203 and the'let-handrepeatinv-coilWindinosY and contacts of' relav- 206.v

h C Y J Rela 107 yreifnains eiierized in series `with Va circuit for relay `209 anda parallel circuit for release relay 210 V*throughA contacts Y ot ,relay 211.A VRelay 209V operates and reverses the connections between the inner rightehand repeatingcoil terminals fand the armatures of vrela-y'211. 2 Relay 210 "places affholding relayl 209.` Relayg211 also connects the Windings of relay 212 to the inner'right-hand repeating-coil terminals through the operated armatures 'of relay 209. As a result, the iiegatiife pole of battery is connected to the lower conductor 'of the trunk line TL2, and

the positive pole of batteryis connected toV the upper conductor. This causes the polarized'linerelay 222 of the trunk circuit TG2,

`which is bridged around the condenser 223,

te operateand close acircuit for lamp 225;v

Relay `225 closes a circuit for the line lamp 227. Y.

Relay 212 inthe trunk circuit-,TC1 dores Anotoperate'inserieswith the polarized relay y y 222 on account, of the high resistance ofthe relay When-both windings are connected' ink series.' i i Y illVhen the `operator notesthe lighted con-` ditionfo'jthe' lamp 227, she-inserts the plug z of airidle cord circuit into the jaclr 228.*Qy .f ilhen'she does'so, current flowsthrough the tipY` and :rin'g'conductors ofthe cordplug and j thrcughthe right-hand' repeating coil Wind` ings in series with the resistance 226, which is i connected up at the inner contacts of relay 225': This giveslthe operator-answering su- Y pervision at herA cordvcircuit in the vusual manner; At its upper armature, relay 221,v

which is Yoperatedover* the sleeve of the ack 228 from the sleeve lof-Lth'efplug, extinguishes y the lainp227 and at its inner armature it short circuits the high-resistanceupperivinding of y relay 222.' VVheiithis occurs, relay 2120iy the trunk circuit TCloperates 'and-completes atits inner-'lower armature a holding Circuit Y for relay 218 through the lower armature of relay211." At its lower contacts,relay 212A y.

closes'a circuit for relay206 through the lower i armature of relay 210.` Relay 206 operates and locks itself at' its'oivn lowery contacts in-- dependentof'th'efloirer coiitactsjof relay 212.v Atits innerllovver armature'andits upper, '-arinature, relay 206v disconnects the incoming conductors 202 and'203V roin'thefwindings of the battery-feed line relav 2021 and 'coni i nects *themV insteadfto the relay'205 througlr therniddle upper armature of relay 210., -Re'-v lay 2021{accord-inglyalls back andk opens the circuit ol relay 209,` but relay209 isnoiv held operated through theiniddle lower armature of relay 20`tgtlie armature or' relay`205, and v 'the lowerfarinature'of relay 210.L Relay/'200 is thus heldoperated and it fniaintains relay 210 operatedatiits lower armature. Y InV this Way the connection isjnoiv held up evenVVV though there is iiocurrent flowing `over `con' vductors 201 vand 208 subsequent toi the disconnection' of relay 204 by Vrelay 206,`

In therep'eaterR', relay 102qA fallsbacl-g l aV result :of the cessatioriof current loiv-fover n the vconductors of the trunk lines TL 1V repon- .j l

sive to the operation voi'vrel'ay' 20601` the trunl-gy y circuit TG1, and completes circuit for re: Vl:5;

ture 113.

lay 208, which includes `contacts controlled .by armature 113 and the inner lower arma-` ture 'of relayA 111. Upon operating', relay 108 closes a circuit for-relay V110 at its upper armature through resistance 109. `Relay 110 operates and closes a new circuit for-relay 111 at its lower arniature',vwhile'at its upper armature it closes acircuit for relay 106.

Relay 106 operates and locks itself at yarinature 112 to the inner lower armature of relayr 111; it shunts the upper contactsof` relay 104 at its upper armature; lopens `a Apointin the circuit ofrelay 105y at its lower armature Yto prevent further operation-ofthe said relay; and at armature 113 it opens the initial`lcircuit of relay 111,' which relay is now held.`

Y, operated-by the lower? armature of relay-'110, `and closes a circuit `for relayV 108,"Which` includes-the' lower armature, operatechofre- Ylay 104 andv armature-113, operatedll't the same time, the initial circuit-of relay 108 1 is opened by the contactscontrolled by armavAs the circuit R, the line relay 104 held energized over [the calling line and is holding the relay 10S" operated.` RelaylOS'is controlling relay 110 and'is at present holding' it operated through the local resistance'lOQ Relay-110 is holding relay 111 operated, Lwhich relayfinaturn is holding' the flockingc'ircuit of relaylOS closed.

1 for a connection which may besetjup right I Forconvenienceinmalnngthe explanation which is to follow-1t will be assumed that the toll recording operator entendstheco-nnection' i away, inlwhich case the 'connect'icnis conifpleted ,through the" toll recordingr switchboard, but if' the. subscriberY asks for' a-{conl nection thatcannOt'be set up immediately,

the toll recording operatorrrecordsthe calling and called numbers andthe callingparty is recalled laterbythe-toll operator. j Y Recalling the operaizorf--VV 'v and that, while the connection-isbeing'extended, the 'calling partydesires to converse againfwith the `toll .recording operator.Y In

order toattract the attention ofthe tollffre'- cording operator, l the callingV subscriber pushes his switchhook down and allows it'to come up again, (repeatingthis a few times in the usual and well lmownmanner. Each time the switchhook ispushed.downy at the callingV substation, line :relay 104 allsback and Y opens the circuit of relay 10S'at-its lower ar-y mature. Relay 108fialls back" and opens 4 the Vlocal circuit of .relay110 th.roughresistance 109, butit'completes a new circuit for relay 110'over the conductorsof the trunk-line T131;

Thelower winding ofrrelay ll0isconnected to the lower conductor of the trunk "line now stands'in therepeater fvisory lanip'tof become Vtors cord circuit.v

The conversation between the callingr sub-` scriber and the toll recordingioperatormay `now proceed. The calling'su-hscriber niay'asl;v

throughthelower contacts of relay 106 and the lower right-,hand repeating-coil winding while the upper winding of'relay 110 is connected to the upper conductor of the trunk line TL1 by way of the normally closed contacts controlledby the upper armature ofrelay 108, innerupper armature ofi-clay 106, upper right-hand repeating-coil windings,

and the uppercontacts of relayy ,1.06.

.WhenV relay Y110 is thus connected to the trunk'line, TL1, current flows over vthe trunk line vr TL1 from the relay'110 and Vpasses through relay 205which is bridged around the condenser 207 through. vcontacts ofv the operated relays 206 and 210.4 Vllpon operating, 'relay 205 opensthe circuit ofrelay l209. then relay i209 falls back it reversesthe connection betweenV the Windingsioffrelayv212 andthe conductors-ofthe trunlline VTL?,i'ivith 'the resultthatthe vpolarized-linerelay '222 restores.fVVhen it doesso, relaylr225 deenergizes and ,opens fthe,"L supervisory ;V bridge through*theresistance 226, causing' thev super- TvVhen the receiver hook is" permitted-to rise esther-calling substation, relay `104 operates lagain and closes-a circuitthrouglrarmature l 113-, operatehfor relay 108;] Relay 1081ope'r- `Qatesfand! closes a loo-p'circuit lfor relay110 throughresistance 109, openingthe circuit of the relay over the Vtrunk',lrinei'IL. When .v this .occurs relayg205-of the trunk circuit TG1 falls back and again closesthefcircuitoflrelay Y* lee V20.9K, whereupon' relayr 209 reoperates'and reversesthe connections between thec'onducin the trunk circuit TG2 'nowresponds and againfo'perates relay 225 to restore Vthe'operators cord circuitto the stateof answered su- Y pervision .I l Y n rThe foregoingropera't'ions are repeated-each mitted torise.

.time the"switchhooklis*depressed land peringtheswitchhoolr are'repeated, and the operators supervisory; lamp lights as a disconlighted the opera-A tors of the trunk line TLzrand the windings Y of the relay212.V The Vpolarized'ilinefrelay, 222

tion, relay-221 falls backend rei-nsertsthev high-resistance iupper'winding, of relay `l222 into thelcircuit. vVihenthisoccurs relayV 212 1n the trunkcircuit TG1 falls back and opens theici'rc'uit of releaserelay 1210.'.Y "Release re- -lay 2 10f falls back a inoinentlate'rand opens the circuity ofrelay 205f'at'itsniiddle `upper armature, whereupon relay205 falls back; at

its innerupper armaturefit opens the circuitV of vrelay `211liandf removes ground from the release 'trunk conductor 202 at its upper armature. lVhen this occurs, the-'selector,S2 re.- v

leases. The circuit-ofrelay 20S:V is opened at the lower armature ofrel`ay210 with the result that-relay 206 -falls bacl':,resto1'1ng the Y trunk circuit to its'normal condition. Y

the trunk line TL1V at the middle upper arma? Tn the repeater R1, relay 110 falls back responsive Ato the opening of its circuitoyer ture ofrelay 210. :Upon restoring, relayl 110 opens the circuitk of relay 111, with the result thatrelay 111 falls back a moment later andl removes ground at itsupper armature Y from release trunk conductor 102. This per-'j mitsthe-line switch y.LS and the selector-S1` to release. Relay v111 at its inner l'owerarmaf ture opens the circuit of relai/'106 and that relayfalls back. VV: f s

Theconnection is now completely released and thel apparatus' involved: therein is ready to be Y used in subsequent@ .connections` It will now beassumed that the connectionv ris set up and thatV the operatorhas responded inVV the manner hereinbefore describedfandthat: the operator `pulls down the connection before the receiveris' replaced at thecalling" substation. `When this occurs, relay 212 of] the trunk circuit TG1, falls backrespons'ive;

to the Areinsertion of the upper high resistance Windingrof relay 222 into its circuit, and it opens the circuit ofrelay210 at its inner low- 'erarmature' asin the releasing operation" previously described. In' this case, however,

`relay 210 doesnot release but is held'operated thelower armature of relay Y209. VRelay by 209, it willberecalled', is now operated in a circuit including the lowerwinding Vof relay 210, lower armature of relay 205, and the middle lower armatureof relay "20G,

Now when the receiver is replaced at the 'calling substation under this condition,V relay 104 falls back andrelayY 10S-falls back as a result and reconnects relay 110 to the conductors of the trunk line 'TL1.K Relay A205 energizes in'series with vrelay'llO and `opens the circuit of relay20 9.` Relay 2209l falls back and opens the` circuit of relayv 210 :itv itslower armature. -R'elay'2l0 falls back andybrings about the release ofthe' selector l S2, its `upper` armature, at .the same time j l Sp1 take placeas hereinbefore.described.

opening fthe circuit over?l the trunk line TL1 for relay 110 at its vmiddle upper armature.v

l v The restorationof the `repeater R- and the release of the line switch'LS andthe selector ,Desc'r'iptiioaofthe l' Referring now parti'cularly'to Fig. 3 the 'modified circuits shown therein will be. explained. The trunk circuitV TG3-is employed l. in theV place of the trunk circuit TG1, andthe `trunk circuitTG isemployedat vthe toll board in place of thetrunk cirouitTG?. "It

vvision through the combined call and dis- 'circuitgtoi be hereinafter traced. y

will` beobseryed that the trunk line JTLB,

which takes the place ofthe trunk-line TLZ,

is a three-conductor trunk line. This comes about lbecause itis assumed that Vthe toll board is located inor near the exchangecontaining the trunk circuit TG3, in Ywhichcase, it` is considered economical to use a thirdV conductorlin the trunk line and simplify the trunk circuit TG3. It has been chosen to 'illustrate the trunk circuit TG4K7 as onegiving superconnect-lamp 326 in addition to-relayingiit into thev cord circuit as is Vthe .ca-se' -of the jv y v trunlcircuit TG2 .of F ig. 2.

1 :The detaileddescriptionof the operation.;

of the apparatus shown in Fig. 3 will now bev given.V I For this purposeit will be'assumed that-thetrunk circuit ,TG3 jisseized by a selec; tor, such; as the selector S? of Fig. y2 over the conductors 301.14303;y VVllhenf this occurs, a

circuit is closed (over conductor 302 `through the test wiper of the-{seizingselector for relay i ngireleaseffrelayin rselector holds up mo` mentarily'afterfits circuit has been opened/'f upon the switchingthrough operation of the f 304. f This comes about because the slow-acti seleetorl As long as the release relay of the selectorcholdsfup, thete'st--wiper is mainey .tained groundedfromrwithin the selector. Uponoperatingrelay304 prepares a locki ing circuitKV for itself `at Vits 'upper armature and at its lower armature prepares a holding As a further-result. of the seizure ofthe .trunk 'circuit TG, a circuit is closed over the series through the left-hand, repeatingfcoil lool incoming talking conductors 301 and3r03 in f windings, normallyclosedcontacts controlled byarmatures of relay 309, right-,hand repeating-coil windings, upper and lower conduc- A .tors ofthe trunk Vline T113, left-hand repeating-coil windings of the 'trunk circuit TG2 and 'through the v windings ofk the line relay 321. -The line relay 321operates and at its upper armature places groundv on. the release trunk` conductorofthetrunk line TLF, yclosing a circuit for relay`i309 ofthe ,trunkV circuit .I TG3, @Relayz309operatesand extends lthe groundedreleasetrunk conductor ofthe trunk line TL3 tothe incomingreleaseitrunl; conductor 302 through the contactsof relay 304."

" This closes a holding circuit for maintaining relay 304 operated, and for holding the' seiz'- parallel, contactsofrelays 301i and 305, lower armature of relay 309,', andthe lower right# hand repeating#coilfwinding.i` This bridge -V maintains relay 321 ofthe trunk circuit T04 i' operated. At the saine time, a bridge excludof sleeve relay 325. v l Y l When the operator responds to the lightedV ing battery and ground kconnections is .closed across the conductors 301 and 303 through the upper :left-hand repeating-coil winding, in-

. ner upper armature ofrrelay 309;"the con?` Y denser 306 and relay 305m parallel,and the Vresponsive to the answering ofthe call by the.

operator. .Y ,v i Y As a furtherresult of the energization 'of line relay 321 of the trunk circuit TCfacii-f cuit Vfor the line lamp 326 is closed at the inner upper armature of the relay through 'cont-acts condition of the lamp 326 by `ii'isertingthe plug of an idle cord circuit .into the jack 327,

, relay 325 pulls up "over the sleeve of the plug in use andof the-jack '327, andfat yits upper' armature makesa second ground connection to the associated release trunk' conductor, and at its innerarmaturey it opens the circuit of the lamp .326; A bridge'is now closed across the tip and ring conductors of the jack through both right-hand windings Aof the repeating coil,` through the condenser 323 A. and the resistance 324 in parallel and contacts 1 35 of relay 321. This bridge permits current to flow, which passes through resistance 324,

giving the operator answering supervision in Vhercord. Y

Recall Y In case the calling subscribermanipulates his switchhook to signal the operator after the operator has responded, the application of i `current to conductorsv 301 Yand 303 by the repeater in use, such as the repeater R, Fig. 1, through the windings of they holding relay,

such as the relay 110, results in the operation of relay 305 of the trunk` circuit TC3.,- When relay 305 operates it opens the circuit of line` relay 321. When line relay 321 alls'back it 1 closes a circuit for the'lamp 326 at itsfinner upper armature, signalling the operator. AtL I Y y 2.v linfa` ytelephone syst-emga trunlrline exits lower armature `it opens the bridgeacross the tip andring conductors ofthe jack, causing the supervisory lampinthecord Icircuit to flash. The release trunk conductor of the trunk line TL3 is maintained grounded at this timeat the upper armature of sleeve relay 325. When the switclihook is Vallowed to 'rise at the calling substationV and-the potential again closes thecircuit `for relay 321. Relay 321 reoperates and extinguishes the lamp "i y 'Release I i to the operation of relay 305 andtheconsequentIreenergizaticn'oti'elay 321. .The disconnect signal is also given in thecord circuit l due to theV opening of the lower contacts of reiaysai. l Y

When the perator pulls downrthe connection, relay 325 falls vbackand removes ground romilthe'associated release trunk conductor at its upper armature7 whereupon relays .308 Y `and309 restore and the preceding'selectorre'- y leases. `Relay 305 lfalls back when relay :309

restores', "T'he "trunk circuits TCS and TC4V are now in normalv condition and the repeater R- clearsjoutf and-permits lthe preceding switches to 4i'eleaseiin the manner' liereinbe-l fore described; e

:nlmyte pointed Outljtiiat the functiiof Assuming nowythat .thecalling'subscriber` replaces his receiver-,l the disconnect signal is l given byfmeans of the lamp k 326 responsive relay 304A is to conditionthe circuit .soi that two-conductor `trunkline,` means including v automatic switching apparatus for extending Va connection to said trunk line by way of said repeater, other automatic switching apparavtheaccidental" grounding of release l rtrunk 'i `conductor302 or the accidental manipulation tus-operable over said trunkiline by impulses A repeated at saidl repeater' to extend a connec# tion from said -trunkline toa called line, said impulses: comprising interruptions in current lowinglina circuit including the two conduc-L f tors ofthe trunkline in series,'mea ns elective after the'connection has been extended to the called line for closing acircuitifor holding the .said-switching apparatus independent of further currentow rover said trunk-line Vand Y for stopping the ycurrent flow over said trunk ine',iand.means for maintaining the current the called line. i 1. Y

vfflow; stopp'ediregardlessjof the condition ofv tendingk from af irst exchange to a 'second' exchange, meansincluding automatic 'switch`V ing: apparatus in fthe `first exchange vfor .ex-

tending-afcoiinection to said trunk line,automatic switching apparatus` inthe second exa l fcurrent .flow tlfi'ereover from Y*a .current source in the ,second .exchangepineansat the first exchange for interrupting the `current iow over. saidtrunlr lineto 1operate the auto- 10' set'upa currentflow th-ereover.y

matic switching'"apparatus inthe second exchange to set up la* connection'fromtbe trunk` line, means effective afterthe connect-ion is set up for stopping the current flow over the trunk line cutting ont the current source vin the second exchange,v and means inrthe first exchange for transmittinga signal to the second exchange by associating a current source in ,the ifirst, exchange with said trunk line,V to

3; In a telephone system, a trunk line extending froma first exchange toi a second exchange, means lnclnding` automatic switching apparatus yin the first exchange forextending aconnecti-onfto'said trunk line auto-v matic switching apparatus in the 'secondiexchange, means :responsive l to the seizure of said trunk line byA the automatic switching appanatns at'the first exchange for lsetting up acurrentrflow thereover froma current source in the second-exchange, means at the first ex-V change for interrupting the-current flow-oven said trunk line to operate the automatic switchingapparatus in theseconjd exchange to set up a connection fromthe `trunk line,V means eitect-ive after the` connection is set Aup for stopping the current However the trunk line hy cutting out the cnrrent source in the second exchange, means in the first exchange for transmitting a signalto the second exchange by associating a current source in the y first exchange with said trunk line to set up a current iow thereover,11fneans-in the second exchange for opening the trunk line to stop the flow of* current thereo'ver, andmeans 1n Y thefirst exchange responsive thereto fory releasing the said automaticswitching apparatus in the first exchange. 1 1.

4. `In a telephone system,v Ia trunk line, means for setting up a current flow over ksaid trunk line and for-interrupting .the current flow, means at the-distantV end ofthe trunk line Aincluding automatic switching apparae tus responsive to the interruptions inthe current iow for extending a connection from the trunk line, means Jfor stopping the current flow over the trunk line, "and vmeans thereafter effective to release the automatic switchingapparatus in the second' exchange responsive -to further current flow lover said trunkn line, and meansl controlled over Ithe connecmamar,

VVheen1extendechmeansfrespnsive'- to further trunk line extending from a first exchange to Y i al second exchange,l Vmeans` fory seizing said trunk linefln the first exchangeyforsetting up arcurrentflow thereover, and orinterruptingfsald currentiiow, means 1n thesecond exchange :mcludmg-automatlc switching apparatus: responsivexto said Jinterruptions" for` setting up a connection from the trunk 'line to a called `line,lmeans effective whenV a response'is 'secured on the called line forstopi Pingl the current flow" OVerJ said Vtrunk s line, means 'controlled fromthe firste'xchange for causing further current flow .over said trunk linermeans in fthegsecond exchange for causing the calledV party .toy be signalled `by the Y urthercurrent fiow,iand means for releasing the `automatic .switches responsive'to `said further current iow ini casethe called partyI has disconnected fromI the. called line.-

4In witness whereofgiIfhereuntosubscribe I my name this 3d dayof A ril, A.D.1929. W g' Y, f VICT 1DSTI-LARI).`v

tion set up through 4the automatic switching Y apparatus for preventing. the release from being eii'ected responsive to said current iiow.V

5. In a telephone system; an inter-exchange trunk line extending from a first exchange to asecond exchange,`means for? seizing said trunk line andfor setting up a current iiow V thereover,means in the first exchange for interrupting Vthe 'currentlow, 'automatic` switching apparatus in the second, exchange responsive to-fsaid interruptions to `extendv a connectionA from the't'runk'line toa called line,` means for stopping"the'currentflow over said trunk line afterthe connection has i L ias 

